This invention concerns a heat-resistant assembly for the water tubes of a heat-exchanger in a boiler to protect them from an atmosphere of super-heated gases, as well as a method of assembling this device.
The water tubes which conduct heat in waste-heat boilers are protected from the heat conducted by the combustion gases and from their corrosive atmosphere by a heat-resistant block.
FIGS. 19 through 21 show several examples of heat-resistant assemblies for the water tubes of a waste-heat boiler taken from the prior art.
The design shown in FIG. 19 was proposed in Japanese Patent Publication (Kokai) 9-184602. In this drawing, 11 are boiler tubes and 13 are flat ribs to lend strength to tubes 11 by connecting them in either a horizontal or a vertical array. 26 are heat-resistant blocks of a ceramic material which are placed so as to protect the tubes 11 from combustion gases 50. The tubes 11 are protected from the heat of the combustion exhaust gases and their corrosive atmosphere 50 by these heat-resistant blocks 26. 23a is a bolt for affixing the heat-resistant block 26 onto one of the flat ribs 13. The bolt 23a extends from the flat rib 13 through heat-resistant block 26. When nut 23b is tightened on bolt 23a, the heat-resistant block 26 is fastened to tubes 11 and ribs 13.
20 is mortar which fills the spaces between heat-resistant block 26 and ribs 13 or tubes 11. 27 is a cap which is placed on top of nut 23b in order to protect the top of the bolt 23a, the portion of the bolt on which nut 23b engages, from combustion gases 50.
FIGS. 20 and 21 show a design proposed in Japanese Patent Publication (Kokai) 9-236203. FIG. 20 is a cross section taken orthogonally with respect to the axes of the tubes. FIG. 21 is a cross section taken along line Axe2x80x94A in FIG. 20. In FIGS. 20 and 21, 11 are the tubes; 13 are the flat ribs which lend strength to the tubes 11 by connecting them; 36 is the heat-resistant block which protects the tubes 11 and ribs 13 from combustion gases 50; and 20 is the mortar which fills the spaces between the heat-resistant block 36 and ribs 13 or tubes 11.
38 is an arm which fixes the block 36 to its rib 13. Arm 38 protrudes from the appropriate portion of the rib 13. When indented portion 37 engages with the arm 38, the heat-resistant block 36 is securely attached to tubes 11 and ribs 13.
Although we do not include drawings, designs for these sorts of heat-resistant assemblies for protecting boiler tubes are proposed in Japanese Utility Patent Publication (Kokai) 1-106706 (Title of invention: Water-cooled Wall) and Japanese Patent Publication (Kokai) 7-225016 (Title of invention: Configuration of Incinerator Walls and Heat-resistant Bricks).
The design proposed in Utility Patent Publication 1106706 features supportive fittings which slant upward on the ribs (or fins) between the tubes and are fixed so that they protrude at specified intervals along the length of the tubes. Indentations are provided on the heat-resistant blocks into which the fittings engage. The spaces between the fittings and indentations are filled with mortar.
In the design proposed in Patent Publication 7-225016, the heat-resistant block (in this case, heat-resistant brick) consists of a number of mantles which have an arc-shaped cross section so that they conform to the contour of the tubes and connective portions which link the mantles. A number of projections are provided on the heat-resistant block at specified intervals along the axes of the tubes so as to maintain the necessary space between the block and the exterior surfaces of the tubes which is to be filled with mortar. Mounting holes are provided in the heat-resistant block into which fittings can be inserted to mount the tubes to the connective portions.
However, the designs described above have the following failings.
In the design proposed in the Patent Publication 9184602, which is shown in FIG. 19, bolt 23a becomes hot when the boiler is operating and undergoes thermal expansion, causing cap 27 to jut out toward combustion gases 50 and separate from the bolt. This results in both the bolt 23a and the nut 23b being exposed to combustion gases 50, which are likely to corrode them. If this corrosion continues over time, heat resistant block 26 will be damaged, or it will separate from the tubes.
And because the heat-resistant block 26 is fastened to boiler tubes 11 and rib 13 by bolt 23a, which is fixed to rib 13 and immobilized, it is constrained when the bolt 23a is tightened. In addition, the thermal expansion differential between tubes 11 and block 26 causes thermal distortion. When this constraint or distortion occurs, the resulting thermal stress and that caused by the temperature differential between the interior and exterior of block 26 will damage the block.
The design proposed in Patent Publication 9-236203, which is pictured in FIGS. 20 and 21, has the potential to solve the problems of the prior art shown in FIG. 19. However, in this device heat-resistant block 36 is supported solely by arm 38, which protrudes obliquely upward from rib 13 and is forced into indentation 37 in the block. This makes it difficult to securely fasten block 36 to tubes 11 and rib 13, and the block 36 has a tendency to slip off the tubes.
With the design proposed in Utility Patent publication 1-106706, just as with that in Publication 9-236203, the heat-resistant block is supported on the tubes solely by a fitting which protrudes obliquely upward from the rib and is engaged in an indentation in the block. This makes it difficult to securely fasten the block to the tubes, and the block has a tendency to become detached.
In the design proposed in Patent Publication 7-225016, just as in that proposed in Publication 9-184602, the end of the fitting which mounts the tubes to the connective portion of the block is exposed to the combustion gases, so it corrodes. If this corrosion is allowed to continue, the block will be damaged or detached from the tubes.
With the prior art designs discussed above, for example that of Patent Publication 9-236203, shown in FIGS. 20 and 21, the heat-resistant block 36 must have an obliquely slanted indentation 37 into which arm 38 of tube 11 can engage. If the angle of inclination of this indentation becomes too large, it will be impossible to remove the block from the mold, and it will not be possible to form the block 36 using a press. Also, in order to attach the block securely, the angle of inclination must be very large. However, a large angle requires that a special mold be used, thereby increasing the production time and the cost.
Such a block 36 is manufactured by pouring the raw material into a metal mold. A molded block is inferior to a pressed block with respect to both strength and durability.
Furthermore, in prior art designs, for example in the design in Patent Publication 9-236203, the space between metal arm 38, which is fixed to tubes 11, and heat-resistant block 36 is filled with mortar to attach the arm 38 to block 36.
The temperature of the area between the arm 38 and block 36 which is filled with mortar rises to 250xc2x0 C. to 500xc2x0 C. The rate of thermal expansion differs widely between metal arm 38 and mortar 20. In prior art devices, then, the differential in thermal expansion between the arm 38 and mortar 20 would damage the mortar, which would have an adverse effect on the durability of the heat-resistant assembly.
With the prior art designs discussed above, the mortar for fastening the tube assembly to the heat-resistant block was introduced into the space between the two. When it approached the required thickness, the worker would use a hand tool such as a trowel to finish filling the mortar to the required thickness according to his own intuition. With prior art designs, then, the final thickness of the mortar would vary with the worker. This caused the durability of different blocks to vary, which sometimes resulted in damage to the blocks.
This invention is an attempt to solve such problems of the prior art as were discussed above.
The first objective of this invention is to provide a design by which the heat-resistant block can be securely attached to the tube assembly consisting of the tubes and the connecting ribs, and which will prevent the block from being damaged or separating from the tubes.
The second objective of this invention is to simplify the process by which the heat-resistant block is assembled or disassembled by making it possible to mount or remove a segment of the block from any portion of the tube assembly.
The third objective of this invention is to prevent the block or its mounting hardware from being damaged by thermal stress or corroded by high temperatures so as to improve the durability of the heat-resistant assembly.
The fourth objective of this invention is to make it possible to manufacture the heat-resistant block using press molding so as to achieve a block with great strength.
The fifth objective of this invention is to prevent the mortar which fills the space between the block and the tube assembly from being damaged by the differential thermal expansion of the mortar and the tube assembly so as to improve the durability of the heat-resistant assembly.
The sixth objective of this invention is to simplify the process of filling the mortar, reduce the number of processes needed to mount the heat-resistant assembly, and make it possible to fill the space between the tube assembly and the block with a uniform thickness of mortar so as to improve the strength of the areas where the mortar is introduced.
To achieve the objectives outlined above, the present invention has been designed so as to comprise the means disclosed in certain preferred embodiments.
In an embodiment, a heat-resistant assembly for protecting boiler tubes is disclosed. This heat-resistant assembly has a heat-resistant block conformed to the contours of the boiler tubes and the surface of their connecting ribs. The boiler tubes and the ribs constitute a tube assembly, and the heat-resistant assembly is placed between the tube assembly and the combustion gases to protect the tube assembly from the combustion gases which are the products of combustion. This heat-resistant assembly is distinguished by the following. It has arms which protrude from the surface of the ribs toward the heat-resistant block and which have catches on their ends. The block has indentations into which the catches on the arms engage. The block can be attached to or removed from the tube assembly by means of the arms and indentations.
In an embodiment, the heat-resistant assembly is further distinguished by the fact that the catches on the arms are formed by bending the ends of the arms which protrude toward the block so that they are angled vertically parallel to the tubes.
In another embodiment, the heat-resistant assembly is further distinguished by the fact that the cross section of the arm will have greater expansion from the tube assembly side towards the heat-resistant block side.
To be more specific, a cross section which goes through the catch on the arm nearer the block will have a greater area than one nearer the tube assembly because a projection is provided on the end of the arm nearer the block. A corresponding indentation is provided on the block. When the projection engages in this indentation, the block is locked to the arm.
In an embodiment, the heat-resistant assembly is further distinguished by the fact that projections are provided on both the upper and lower ends of the heat-resistant block. One of these projections is on the side of the block which faces the combustion gases; the other is on the side which faces the tubes. When the blocks are stacked vertically, the projection on the gas side of one block will face the projection on the tube side of the next block.
In an embodiment, the heat-resistant assembly is further distinguished by the fact that the catches on the arms are formed by bending the ends of the arms which project toward the block so that they are angled vertically parallel to the tubes. The force of gravity will cause the block to descend so that the vertical catches can engage in its indentations. In addition, one projection is provided on the upper end of the block on the side facing the combustion gases and a second projection is provided on the lower end of the block on the side facing the tubes.
The heat-resistant blocks are interlockingly fastened or attached to the tube assembly by arms on its ribs which are made to engage in indentations in the heat-resistant block taking advantage of the gravitational force exerted by the weight of the block. There is no need for bolts or nuts as were used in the prior art, which may protrude into the chamber filled with combustion gases. Thus there is no possibility of high-temperature corrosion.
Because the arms have vertical end portions which are parallel to the tubes, the blocks can be fastened to the tube assembly using the weight of the block so that they can be freely removed or replaced even if the tube assembly consisting of the tubes and their connecting ribs is located at the top end where no upper space is left.
Since there is no need for locking mechanisms such as the nuts and bolts employed in prior art devices, and the means used to fasten the blocks to the tubes allow them to be removed or replaced, there is no possibility of thermal constraint between the tubes and the block. As a result, the block can be made much thinner. The temperature differential between the interior and exterior of the block will be much smaller, the temperature of the block will not spike, and the block will experience less thermal stress.
Providing projections on both the upper and lower ends of each block segment, with the upper projection on the side that faces the combustion gases and the lower projection on the side that faces the tubes, has the effect of modularizing the block, so that for example a single segment (or set of segments) could be removed. This design makes it possible to repair portions of the block and simplifies maintenance.
Placing projections on the upper and lower ends of each heat-resistant block segment, one on the side of the block facing the combustion gases and the other on the side facing the tubes, ensures that spaces will be provided for thermal expansion of the block and prevents the extremely hot corrosive gases in the combustion gas chamber from coming in contact with either the tubes or the interlocking mechanism consisting of the arm and indentation.
In an embodiment, the heat-resistant assembly is further distinguished by the fact that a space is provided at least between the end of the arm and the indentation of the block. In the space is placed a fusible substance which will melt when the temperature of the arm exceeds a given value.
With this invention, if the metal arm which is a component of the tube assembly exceeds a specified temperature, say 250xc2x0 C., while the boiler is operating, the fusible substance placed in the space will melt, thereby creating a new expansion space.
The space, then, accommodates the expansion which the arm undergoes as its temperature rises. In other words, it is a gap which allows for thermal expansion of the arm. This prevents the mortar from being damaged by the differential between the rates of thermal expansion of the arm and the mortar.
A suitable choice for the fusible substance might be rubber tape. Alternatively, the space could be filled with paint.
In an embodiment, a heat-resistant assembly for protecting boiler tubes is disclosed. This heat-resistant assembly has a heat-resistant block conformed to the contours of the boiler tubes and the surface of their connecting ribs. The boiler tubes and the ribs constitute a tube assembly, and the heat-resistant assembly is placed between the tube assembly and the combustion gases to protect the tube assembly from the combustion gases which are products of combustion. This heat-resistant assembly is distinguished by the following. An arm with a catch on its end projects from the surface of the rib toward the heat-resistant block. An indentation is formed in the block facing the rib. A locking means such as a sleeve, which is formed by a press to ensure that it will have sufficient strength, is adhered into the indentation. The heat-resistant block is fastened to the arm by the locking means.
In an embodiment, the heat-resistant assembly is further distinguished by the fact that the locking means is made of a heat-resistant substance of the same silica family as the heat-resistant block, and the adhesive agent is a high-temperature adhesive which can tolerate the heat of the locking means.
To mount the heat-resistant block to the arm of the tube assembly, a heat-resistant sleeve is first inserted into the indentation in the block opposite the rib. The outside surface of the sleeve is coated with a high-temperature adhesive, and the sleeve is attached (i.e., cemented) to the heat-resistant block. When the arm engages in the heat-resistant sleeve, the block is fixed to the tube assembly in the same fashion that a picture is hung on a wall.
With this invention, the heat-resistant block itself has no interlocking mechanism by which it is directly attached to the arm, but only an indentation opposite the rib. This indentation can be formed when the block is pressed, so it is possible to release the press die from the pressed block, and thus possible to manufacture the entire block using a press process.
A heat-resistant block can thus be achieved which is extremely strong because it is formed by a press.
The use in the locking means of a heat-resistant sleeve composed of silicon carbide vastly increases the strength of the mount.
Since the heat-resistant block is also composed of a material in the silica family such as alumina, silica or silicon carbide, it is made of the same sort of substance as the sleeve. The rates of thermal expansion of the block and the sleeve will be similar, and the block will not warp.
The adhesive which is used is one whose adhesive strength is not affected at temperatures in excess of 250xc2x0 C. such as phosphoric acid mortar or Allonceramic (trade name). Thus there will be no loss of adhesion at high temperatures.
In an embodiment, the fastening method for fastening a heat-resistant assembly for protecting boiler tubes is disclosed. This heat-resistant assembly has a heat-resistant block conformed to the contours of the boiler tubes and the surface of their connecting ribs. The boiler tubes and the ribs constitute a tube assembly, and the heat-resistant assembly is placed between the tube assembly and the combustion gases to protect the tube assembly from the combustion gases which are the products of combustion. Mortar is used to fasten the heat-resistant blocks on the tube assembly. This method of fastening the heat-resistant assembly on the tube assembly is distinguished by the following. When the mortar is provided onto the depressed portions of the exterior surface of the tube assembly, the application process is divided into two steps: applying the mortar to the tube assembly, and applying the mortar to the block. Once the mortar has been applied to specified portions of the block and tube assembly, the two surfaces are cemented together through the adhesive strength of the mortar. In this way the tube assembly and heat-resistant block are attached to each other by the mortar.
The mortar is applied uniformly to the exterior surface of the tube assembly, including the depressed portions. In addition, the application process is divided into two steps: applying mortar to the tube assembly and applying mortar to the block. Since the mortar is applied to exposed spaces, no expertise is required. Also, because the spaces are exposed, the mortar can be applied to the specified thickness using a gauge such as a scraper.
The mortar is applied to the depressed portions of both the tube assembly and the block. The protruding portions (the opposed straight line along the tube assembly and straight flat portion of the block facing the ribs) can be used as guide surfaces in the scraping operation.
In another embodiment of this application, a fastening method for fastening a heat-resistant assembly for protecting boiler tubes is disclosed. This heat-resistant assembly has: a tube assembly having a number of tubes and the ribs which connect the tubes; a heat-resistant block conforming to the contour of the exterior surfaces of the tubes and ribs; interlocking mechanisms projecting from the surfaces of the ribs toward the block; and indentations on the surface of the block into which the interlocking mechanisms engage. This fastening method is distinguished by the fact that it entails the following processes.
It has a first process to control the thickness of the mortar, in which the excess mortar, which has been applied to the ribs connecting the contiguous tubes, is removed with a scraper using the exterior surface of the tubes as a guide;
In an embodiment, the fastening method for fastening a heat-resistant assembly is further distinguished by the fact that the portions where the mortar is to be applied to the tube assembly and the heat-resistant block are the indentations between contiguous tubes on the tube assembly, and the indentations on the curved interior surface of the block facing the exterior of the tube assembly on the heat-resistant block. a second process to control the thickness of the mortar, in which the excess mortar, which has been applied between the curved indentations on the block opposite the exterior surface of the tubes, is removed with a scraper using the flat straight surface of the block which faces the ribs as a guide; and a third process for cementing, in which the indentations on the block which have been filled with mortar in specified locations are brought in contact with the interlocking mechanisms on the tube assembly, so that the mortar causes the two surfaces to adhere to each other. Through these processes, the tube assembly and the block are cemented to each other by means of mortar.
In another embodiment, the excess mortar, which has been applied to the indentations between the tubes, is removed from the curved inner surfaces with a curved scraper whose shape conforms to the outer surface of the tube, and the excess mortar, which has been applied between the outside of the tube and the curved inner surface of the block opposite the tube, is removed with a scraper using the flat straight surface of the block opposite the rib as a guide. Not only the excess mortar on both the block and the tube assembly, but also that on the curved inner surfaces, is removed by a scraper with two concavities in its working edge. The operation of scraping off the excess mortar is made much easier, and fewer processes are required to construct a heat-resistant assembly for protecting boiler tubes.
Because the exterior surface of the tube and the flat straight part of the heat-resistant block are used as guides for the scraping operation, the mortar can be finished to a precise thickness.